Production of gem-difluoroalkenes



United States Patent US. Cl. 260-6535 9 Claims ABSTRACT OF THE DISCLOSURE Gem-difiuoroalkenes are produced by dehydrohalogenating 1,1,1-difiuorohaloalkanes in the presence of low surface area alumina. Improved results are obtained by the use of low surface area alumina containing at least one metal promoter.

This invention relates to the production of gem-difluoroalkenes. In one aspect, it relates to the production of 1,1-difluoroalkenes by the dehydrohalgenation of 1,1-difluoro-l-haloalkanes over a low surface area alumina catalyst. In another aspect, it relates to the production of l,l-difluoroalkenes by the catalytic dehydrohalogenation of 1,1-difluoro-1-haloalkanes by contacting them with a low surface area alumina catalyst. In another aspect, it relates to the production of gem-difiuoroalkenes by contacting 1,1-difluoro-l-haloalkanes with low surface area alumina catalyst in the presence of metal or metal compound promoters. In another aspect, it relates to the dehydrohalogenation of 1,l-difluoro-l-haloalkanes over a low surface alumina catalyst to produce a 1,1-difluoroalkene with a minimum of side reactions. In still another aspect, it relates to the production of 1,1-difluoroethylene by the dehydrochlorination of 1,1-difluoro-l-chloroethane, substantially free of side reactions, by contacting the starting material with a low surface area alumina.

The dehydrochlorination of 1,1-difluoro-l-ch1oroethane and similar compounds over alumina containing catalysts is well known in the art. Various other catalysts, including aluminum fluoride, charcoal and various metal compounds have also been used in such a dehydrohalogenation reaction. However, a number of side reactions also occur under the dehydrohalogenation conditions, and the product of the reaction is a mixture of fluoroand chloro-containing compounds both saturated and unsaturated. The major product of such a reaction is generally an unsaturated fluoro-c-hloride. Gem-difluoro compounds are usually produced in such reactions, but they are usually produced in low yield, and must then be separated from the various other chloro and fiuoro compounds which are also formed.

It is therefore an object of this invention to provide a method for producing a gem-difluoro compound substantially free of other fiuorinated and chlorinated products. It is another object of this invention to dehydrohalogenate a 1,1-difluoro-1-haloalkane to produce a gemdifluoroalkene. It is still another object of this invention to produce a relatively pure gem-difluoroalkene by dehydrohalogenating a 1,l-difluoro-l-haloalkane. It is yet another object of this invention to produce 1,1-difiuoroethylene from 1,l-difiuoro-Lchloroethane with a minimum of side reactions.

According to the invention, a gem-difluoroalkene is produced by contacting a 1,1-difluoro-1-haloalkane with low surface area alumina under dehydrohalogenation conditions.

The use of a relatively low surface area alumina is essential to the operation of my invention. Preferably, the alumina is alpha-alumina. However, any alumina having a surface area below about 50 square meters per gram can be used. For example, etaor gamma-alumina Cir 3,444,251 Patented May 13, 1969 which has been heated suificiently to reduce the surface area below about 50 square meters per gram can be used. Use of an alumina having a higher surface area than 50 square meters per gram will encourage side reactions and result in a product mixture difficult to separate in order to obtain pure gem-difiuoroalkenes.

The starting materials useful in the process of my invention have the general formula R CHCF X, where R is hydrogen or an alkyl radical preferably having 1 to 8 carbon atoms, the total number of carbon atoms in the molecule preferably does not exceed 1.0, and X is chlorine or bromine.

Some examples of compounds which are useful in the process of my invention are:

1, l-difluorol-chloroethane l,l-difluoro-l-bromoethane 1, l-difluorol-chloro propane l, l-difluorol-bromobutane l, l-difluorol-chlorohexane l, l-difluoro-l-bromooctane l 1difiuoro-1-chlorodecane l, l-difluorol-chloro-2-methylpropane 1,1-difiuoro-l-bromo-S-methylbutane l, l-difluorol-chloro-4-ethylhexane l, l-difluorol -bromo-2-ethylbutane 1,l-difluoro-l-chloro-3,3-dimethylbutane Preferably, the alumina of low surface area contains a metal .promoter which facilitates the conversion of the l,l-difluoro-1-haloalkane to the 1,1-difluoroalkene. Examples of applicable metal promoters are zinc, chromium, cobalt, silver, copper, vanadium, iron, molybdenum, nickel, lead, antimony, tin, ruthenium rhodium palladium, osmium iridium, and platinum. The metal promoter can be used either as the free metal or as a compound thereof. If desired, two or more metal promoters can be used. The metal promoter can be incorporated in the alumina by well-known methods such as grinding a salt, oxide, or other form of the metal with the alumina. A preferred method of preparing the catalyst involves impregnation of the alumina with a solution containing the metal compound. Metal compounds which are usable include the oxides, fluorides, chlorides, bromides, iodides, nitrates, and fluoroborates of zinc, chromium, cobalt, silver, copper, vanadium, iron, molybdenum, nickel, lead, antimony, tin, ruthenium, rhodium, palladium, osmium, iridium, and platinum.

When the alumina of low surface area contains a metal promoter, the concentration of the metal promoter, expressed as the concentration of the free metal, generally is not greater than about 50 Weight percent of the catalyst composite, usually being not greater than about 30 weight percent of the catalyst composite. When ruthenium, rhodium, palladium, osmium, iridium, or platinum is used as the metal promoter, the concentration of metal promoter, expressed as the concentration of the free metal, is usually not greater than about 1 weight percent.

Although the reaction temperature employed in the process of this invention can vary over a broad range, it will generally be within the range of about 300-1200" F., usually being within the range of about 6001000 F. The flow rate of the 1,1-difiuoro-1-haloalkane, expressed as the flow rate of the l,l-difluoro-l-haloa1kane in the gaseous state, will generally be within the range of about 20- 2000 volumes (standard conditions) per volume of catalyst per hour, usually being within the range of about 50- 500 volumes (standard conditions) per volume of catalyst per hour. If desired, an additional amount of an inert diluent or carrier such as nitrogen, helium, argon, or the like can be present with the l,l-difluoro-l-haloalkane. Although the total pressure is conveniently maintained at substantially atmospheric, pressures somewhat above or below atmospheric can be employed. Usually the total pressure will be within the range of about 0.1-20 atmospheres, preferably being within the range of about 1-5 atmospheres.

The 1,1-difluoroalkene is readily separated from other 4 to products other than 1,1-difluoroethylene, the latter compound being produced only in minor amounts. It is to be noted that unreacted 1,l-difluoro-l-chloroethane will be recycled to the catalyst, and thus will eventually be com pletely reacted. Thus, although the yield of 1,1-difluorocomponents of the effluent from the process of this inven- 5 ethylene is low per pass through the catalyst, the ultimate tion by conventional techniques such as distillation, chroi 1d ill b quite hi h, d h product formed i11 h p yr and the like, Preferably after removal of a much higher concentration of 1,1-difluoroethylene than hydrogen halides, 8-, With Water or an aqueous Solution the product formed with any other catalyst in this exof caustic. 10 ample Examples of some 1,1-difiuoroalkenes which can be pro- Example 11 duced by the process of thls mventlon mclude' A gaseous stream of l,ldifluoro-l-chloroethane was l,l-difluoroethylene passed at atmospheric pressure through a l-in. x 12-in. 1,1-difiuoropropene tubular reactor packed with 100 ml. of a catalyst com- 1,1-difluoro-1-butene 15 prising alpha-alumina promoted with nickel or zinc or a 1,1-difluoro-1-hexene catalyst comprising cobaltand molybdenum-promoted 1,1-difiuoro-1-octene alumina of low surface area. The nickelor zinc-promoted 1,1-difiuoro-1-decene catalysts were prepared by impregnation of alpha-alumina l,l-difiuoro-2-methylpropene with an aqueous solution of a nickel or zinc salt, followed l,l-difiuoro3-methyl-l-butene by draining of the excess solution from the catalyst, drying yl-l-hexene of the catalyst, and heating of the catalyst at 9501000 1,1-difi110I0-2-ethY1-l-blltehe F. overnight in a stream of nitrogen. The cobaltand fi' y molybdenum-promoted alumina (Girdler T-305; Girdler Catalyst Division, Chemetron Corp.) had a surface area Examp 16 I of 26 square meters per gram. The flow rate of the 1,1- A gaseous stream of Ll-difluoro-l-clfloroethane was CllflilOIO-l-ChlOIOCllhflIlfi was maintained at 60-100 volumes passed at atmospheric pressure through a l-in. x 12-in. P Volume of Catalyst P hohf- The Catalyst temperature tubular reactor packed with 100 ml. of various catalysts. WES a t d a F. The I ehhleht Was Passed The flow rate of the 1,l-difluoro-l-chloroethane was main- 30 through water to remove hydrogen halides, and the hydrotained at 60-100 volumes per volume of catalyst per gen halide-free product was dried and analyzed gas chrohour. The catalyst temperature was maintained at 700 F. matographically, identification of the components being The reactor effluent was passed through water to remove obtained with the aid of mass spectrometry. The results hydrogen halides, and the hydrogen halide-free product of these runs are summarized in Table II, the mole perwas dried and analyzed gas chromatographically, identificent of each component in the effiuent being rounded off cation of the components being obtained with the aid of a to the nearest whole number.

TABLE II Metal promoter on Composition of dried, hydrogen halide-free efliuent, mole percent alumina support,

wt. percent CHaCFgCl CH2=GF 0133013. CH =CFO1 CH2=CCl2 so 10 a 8 0 54 as 3 5 0 52 as 3 s 0 52 33 9 6 0 33 (ii 2 5 0 Impregnation oi alpha-alumina was carried out with an aqueous solution containing 88.0 g. of NlClzzfiHzO per 100 ml. oi solution. I

1 Impregnation of alpha-alumina was carried out with an aqueous solution containing 108 g. oi Ni(NO3)26I-I2O per 100 ml. of solution.

3 Impregnation oi alpha-alumina was carried out with an aqueous solution containing 45.3 g. oi ZnClz per 100 ml. oi solution.

4 Impregnation of alpha-alumina was carried out with a weight percent aqueous solution of Zn(BFi)2.

Thus, the use of each of the promoted catalysts resulted in the formation of 1,1-difluoroethylene as the principal reaction product.

Example III The catalysts used in Example II were employed in TABLE I Composition of dried, hydrogen halide-free effluent, mole, percent Catalyst CHzCFzCI CH=CF3 CH.-,CF CH= CF01 CH2=CC12 Gamma-alumina 0. 5 6 0 85 0 Gamma-alumina 0. 2 11 22 30 32 Aluminum fluoride 10 4 43 22 22 Fluorided gamma-alumina 3 0.6 0. 2 48 2 49 Alpha-alumina 4 94 3 0. 8 2 0 1 Fresh catalyst. Surface area approximately 200 square meters per gram. 1 Alter 10 hours on stream. Additionally, the dried, hydrogen halide-tree effluent formed with this catalyst contained 5 mole percent oi unidentified material.

I Prepared by passing a dry stream of hydrogen fluoride containing 50 volume percent nitrogen over dried gamma alumina for 4 hours, during which time the temperature of the catalytic material rose from an initial value of about 300 F. to a maximum value of 650 F.; the flow rate 01 the hydrogen fiuoridenitrogen mixture was 200 volumes per volume of catalyst per hour. The resulting fiuorided alumina catalyst contained 51.6 weight percent fluorine and had a surface area of 25 square meters per gram.

4 Suriace area less than 1 square meter per gram.

Thus, the use of alpha-alumina in the catalytic conversion of l,l-difluoro-l-chloroethane resulted in the formation of 1,1-difluoroethylene as the principal reaction product, other substances being formed in lesser amounts. In contrast, the other aluminum-containing catalysts caused another group of runs designed to produce l,l-difluoroethylene from l,l-difluoro-l-chloroethane in the same procedure and under the same conditions used in Example II except that the catalyst temperature was maintained at 900 F. Also investigated under these conditions was a the 1,l-difluoro-l-chloroethane to be converted primarily rhodium-promoted catalyst prepared by impregnation of alpha-alumina with an aqueous solution of rhodium chloride, with subsequent draining, drying, and heating of the catalyst by the procedure used for the other impregnated catalysts. Additionally, alpha-alumina Without a promoter and fluorided gamma-alumina were investigated as dehydrochlorinating agents under the same conditions. The results of these experiments are summarized in Table III, the mole percent of each component in the dried, hydrogen halide-free eflluent being rounded off to the nearest whole number.

surface area alumina having a low surface area of less than about 50 mF/gram at a temperature between 300 F. and 1200 F.

2. Process of claim 1 wherein said contacting occur at a temperature between 600 F. and 1000 F.

3. Process of claim 1 wherein said 1,1-difluoro-l-haloalkane is in the vapor phase during said contacting.

4. Process of claim 1 wherein said 1,1-difluoro-l-haloalkane is in the vapor phase during said contacting and is diluted with an inert gas.

TABLE 111 Metal promoter on Composition of dried, hydrogen halide-free effluent, mole percent alumina support,

wt. percent CHaCFzCl CH2=OF1 CH CF CH2: CFC] CH=CC11 Ni, 5 l 63 3 9 0 Ni, 5 14 76 3 7 0 Zn, 5

4 s2 2 12 0 Zn, 2.7 13 74 5 9 0 Rh, 0.2 5 B 76 4 13 0 Co, 9.0; Mo, 18.5 2 71 11 16 0 Alpha-alumina only 46 45 2 7 0 Fluorided gamma-alumina 1 17 30 12 I See footnote 1 to Table II. 2 See footnote 2 to Table II. a See footnote 3 to Table II. 4 See footnote 4 to Table II.

5 Impregnation of alpha-alumina was carried outwith an aqueous solution containing 1.27 g. of RhCl; per

100 ml. of solution.

6 Girder T-305 catalyst comprising cobaltand molybdenum-promoted alumina; surface area, 26 square meters per gram.

7 See footnote 3 to Table I. No alpha-almnina support was used.

As in Example I, the alpha-alumina employed in EX- amples II and III had a surface area of less than 1 square meter per gram.

Thus, the use of alpha-alumina, with or without a metal promotor, resulted in the conversion of 1,1-difiuoro-1- chloroethane at 900 F, to give 1,1-difluoroethylene as the principal reaction product. In contrast, 1,1-difluoroethylene was a minor product when fluorided gammaalumina was used as the catalyst.

When 1,l-difluoro-1-chloroethane Was passed at atmospheric pressure through the same tubular reactor, in the absence of a catalyst, at 900 F. at a fiow rate of 100 volumes per volume of reactor per hour, 93 mole percent of the 1,l-difiuoro-l-chloroethane remained unconverted.

Reasonable variation and modification are possible within the scope of the foregoing disclosure, and the appended claims to the invention, the essence of which is that a gemdifluoroalkene is produced by contacting a 1,1-difiuoro-1- haloalkane with low surface area alumina under dehydrohalogenation conditions.

I claim:

1. A process for producing a gem-difluoro-alkene comprising contacting a 1,1-difiuoro-1-haloalkane of the formula R CHCF X, wherein X is selected from chlorine and bromine, R is selected from hydrogen and alkyl radicals having 1 to 8 carbon atoms, and the total number of carbon atoms in the alkane does not exceed 10, with low 5. Process of claim 1 wherein said catalyst contains a promoter selected from zinc, chromium, cobalt, silver, copper, vanadium, iron, molybdenum, nickel, lead, antimony, tin, ruthenium, rhodium, palladium, osmium, iridium, platinum, and compounds thereof.

6. Process of claim 1 wherein said alumina comprises essentially alpha-alumina.

7. Process of claim 1 wherein said 1,1-difluoro-1-haloalkane is 1,l-difluoro-l-chloroethane.

8. Process of claim 1 wherein said l,1-difiuoro 1-haloalkane is 1,l-difluoro-l-chloroethane and said catalyst contains a promoter selected from salts of nickel, zinc, cobalt, molybdenum and rhodium.

9. The process of claim 1 wherein said alumina has a surface area of less than about 1 m. gram.

References Cited UNITED STATES PATENTS 2,478,933 8/1949 Bratton et a1. 260653.5 3,118,005 l/1964 Pavlath ct al 260653.5

DANIEL D. HORWITZ, Primary Examiner.

US. Cl. X.R. 

